JPS6224681A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce the thermal resistance of a clad layer without deteriorating the light confinement and improve heat radiation to unnecessitate forced cooling and obtain an InGaAlP semiconductor laser facilitating continuous oscillation of a low current at the room temperature by specifying the thickness of an InGaAlP activation layer and the thickness of the InGaAlP clad layer of the heat sink side. CONSTITUTION:The thickness of an InGaAlP activation layer 13 is selected to be 0.1-0.3mum and the thickness of an InGaAlP clad layer 12 of the heat sink 19 side is selected to be 0.8-0.3mum. For instance, after the N-type In0.49 Ga0.31Al0.20P clad layer 12, the In0.49Ga0.51P activation layer 13, a P-type In0.49 Ga0.31Al0.20P clad layer 14 and a P-type GaAs cap layer 15 are successively formed to the thicknesses of 0.5mum, 0.2mum, 0.5mum and 1mum respectively on an N-type GaAs substrate 11 by a molecular beam epitaxial method, an SiO2 film 16, a P-type electrode 17 and an electrode 18 are formed and then an SiO2 stripe laser with a stripe width of 5mum and a resonator length of 200mum is obtained by cleaving and mounted on the heat sink 19.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a compound semiconductor laser, and more specifically, the invention relates to a compound semiconductor laser having a wavelength of 0.58 μm to 0.68 μm.
This invention relates to an InGaA1p semiconductor laser that emits visible light.

BACKGROUND OF THE INVENTION Currently, various semiconductor lasers have been developed and put into practical use. Among these, semiconductor lasers that emit continuous light have also been developed and are used in various devices. For such continuous light emission, it is desirable to drive the semiconductor laser with a small operating current and a small operating current density. In order to achieve high optical amplification under such conditions, it is preferable to make the active layer as thin as possible, and making the active layer as thin as possible increases the coupling efficiency with the optical fiber. The above is also preferred.

In order to efficiently emit light with such a thin active layer as described above, it is necessary to confine carriers within the active layer and also confine emitted light within the active layer. To achieve this, it is necessary not only to simply make the active layer thinner, but also to increase the energy gap difference between the active layer and the cladding layer.
It is also necessary to increase the difference in refractive index between the active layer and the cladding layer. By doing so, a high injected carrier density, that is, a high gain, can be obtained with a small current, and emitted light can be confined in the active layer.

On the other hand, as a semiconductor laser for visible light, an InGaAlP semiconductor laser, which is a quaternary compound semiconductor laser, has been developed in recent years. The 1nGaAI P semiconductor laser is usually formed on a GaAs substrate for lattice matching, and the active layer is In0. 49Ga0. s, -XAl-P (
0≦x<0.3) layer is made of In0. 4
sGa0. s+-yAly P(x+0.2≦y≦0
．． 51) It has a sandwiched structure.

FIG. 3 shows an example of the structure of this semiconductor laser. The illustrated semiconductor laser has a GaAs substrate 1 on which In0. 4sGa0. An n-shaped rad layer 2 of s+-yAly P, [n0. 49Ga0. s+-
An active layer 3 of xAlxP, ln0. 4sGa0.
A p-type rad layer 4 of s+-yAly P is formed in that order, and a cap layer 5 is further provided. Electrodes 6 and 7 are formed on the cap layer 5 and the substrate 1.

In the above InGaAl P semiconductor laser,
As mentioned above, in order to achieve high luminous efficiency with a small operating current, the thickness of the active layer has been set to about 0.3 μm or less. However, since the refractive index of 1nfiaA]P is unknown, the cladding layer 2.
The thickness of the 7th part of 4 was increased to more than 1 μm. However, 1nG
aA] P has poor thermal conductivity compared to GaAs, etc., and heat dissipation from the active layer 3 through the 1nGaAI P cladding layer with high thermal resistance is not sufficiently carried out, making it difficult to continuously operate at a low drive current at room temperature. I couldn't get it to oscillate. Therefore, in order to use it in continuous oscillation, a forced cooling device is required, which not only increases the size of the device but also has the disadvantage that it cannot be easily applied.

Problems to be Solved by the Invention As mentioned above, in the conventional InGaAlP semiconductor laser, the cladding layer must be considerably thick in order to exhibit a sufficient optical confinement effect, so heat dissipation is poor. This was not sufficient, and continuous oscillation could not be achieved as it was, so forced cooling was required.

Therefore, the present invention aims to improve heat dissipation by lowering the thermal resistance of the cladding layer without impairing optical confinement, and to achieve low current continuous oscillation at room temperature without the need for forced cooling.
The present invention aims to provide a P semiconductor laser.

Means for Solving the Problems The inventors of the present invention have conducted various studies for the above purpose, and have
n0. <5Ga0. s + -, Al
．． 2, the refractive index difference was found to be approximately 0.2.

FIG. 2 shows In0. 4 gGa0. s + - x81
3 is a graph showing the relationship between the refractive index of P and the energy of incident light. In the graph of Figure 2, approximately 1.82 e
V corresponds to a wavelength of 0.68 μm, and 2.14 e
V corresponds to a wavelength of 0.58 μm.

On the other hand, in order to enable laser oscillation, it is necessary that the energy dissipated from the planar waveguide consisting of the cladding layer and the active layer be sufficiently low. In the structure of a semiconductor laser as shown in FIG. 3, once the refractive index of each layer is determined, the solution of the waveguide mode can be found using the electromagnetic wave equation. In this solution, the propagation energy confined in the cladding layer and the active layer of the total optical energy can be determined by calculation. Conversely, it is also possible to determine the thicknesses of the active layer and cladding layer necessary for a certain level of light confinement.

For example, the solution for the transverse electromagnetic field mode when the cladding layer has a semi-infinite thickness is expressed by the following equation (1).

...(1) Here, y is the distance from the midpoint of the active layer in the direction perpendicular to the active layer, E is the electric field component perpendicular to the optical axis, and d is the thickness of the active layer. It is. Furthermore, T and K are eigenvalues that satisfy the following equations (2) and (3).

N γ Here, K is the oscillation wave number of the laser, and n is the oscillation wave number of the laser.

is the refractive index of the active layer, and D is approximately the difference in refractive index between the cladding layer and the active layer. Therefore, when the thickness of the cladding layer is limited to L, the light confinement rate F in the active layer is
It can be determined approximately from the following equation (4).

According to the inventors' calculations based on this and the inventors' research results on the refractive index, the layer structure of the semiconductor laser is as follows:
If the active layer thickness d is set to 0.1 to 0.3 μm to ensure sufficient light emission and emit light with low power consumption, 99.9% or more of optical confinement can be achieved with a cladding layer of 0.8 to 0.3 μm. I found out that it is possible.

Therefore, even if the cladding layer is thinned to the extent that optical confinement is possible, laser oscillation is not affected.

The present invention has been made based on this knowledge.

That is, according to the present invention, In0. n5Ga0
．． An active layer consisting of 51-1+"81.P (0≦X<0.3) and ln0.4s provided on each side of the active layer.
Ga0. s+-yAly P (x +0.2≦y≦
The 1nGa8P active layer has a thickness of 0.1 to 0.3μm, and has a cladding layer composed of The thickness of the InGaAlP cladding layer is 0.
InGaAl characterized by having a diameter of 8 to 0.3 μm
A P semiconductor laser is provided.

In the InGaAl P semiconductor laser as described above,
As described above, the difference in A1 composition between the active layer and the cladding layer is 0.2. This difference in A1 composition of 0.2 is a value that provides a sufficient energy gap difference to confine injected carriers within the active layer, and therefore light can be emitted with sufficient efficiency. On the other hand, in the emission wavelength range of 0.58 to 0.68 μm of the InGaAlP semiconductor laser, the refractive index of the active layer can be set to about 3.6 by the above composition, and the difference in A1 composition between the active layer and the cladding layer is 0. .2, the refractive index difference between the active layer and the cladding layer in the light emitting region of an nGaAl P semiconductor laser is approximately 0.
, 2. Therefore, even if the cladding layer has a thickness of 0.3 to 0.8 μm as described above, light can be sufficiently confined within the active layer.

Therefore, when a voltage is applied to the active layer through the cladding layers that sandwich the active layer, carriers are confined within the active layer due to the energy gap difference between the active layer and the cladding layer, and efficient light emission is realized. The light thus emitted is confined in the active layer due to the difference in refractive index between the active layer and the cladding layer.

By making the cladding layer thinner,
The thermal resistance of the entire cladding layer can be reduced, and the thermal characteristics of the sheet can be improved. Additionally, continuous light emission can be performed without forced cooling.

Embodiments Hereinafter, embodiments of a semiconductor laser according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view of an embodiment of a semiconductor laser according to the invention. The illustrated semiconductor laser has an n-type GaΔS substrate 11, and on the substrate 11 (Inn with a thickness of 0.5 μm, <5Ga0.3181
0.20 P n-shaped rad layer 12 and a thickness of 0.2 μm
In0. 4sGa0. An active layer 13 of s+'P and an In0. 49 (ia0. 31A
A p-type rad layer 14 of I0.20'P and a thickness of 1 μm.
and a p-type GaAs cap layer 15 are formed in that order. Then, on the GaAs cap layer 15,
A 5i02 film 16 is provided with a striped opening of 5 μm in width and 200 μm in length, and a p-type electrode 17 is provided on top of the 5i02 film 16, and a GaAs cap layer 15 and a p-type electrode 17 are provided on the SiO□ film 16. Ohm contact. Further, an n-type electrode 18 is formed on the top curve of the n-type GaAs substrate 11, and is mounted on a heat sink 19 via the electrode 18. Thus, SiO with a stripe width of 5 μm and a cavity length of 200 μm. A striped laser is configured.

The semiconductor laser described above is manufactured by, for example, depositing n-type Ga onto an S substrate 11 using a molecular beam epitaxial method.
n0. n, Ga0. 3+A10. 20 P cladding layer 12 with a thickness of 0.5 pm, In0. 4sG
a0. The slP active layer 13 has a thickness of 0.2 μm and is made of p-type In0. 4Ja0. 31810.20 P cladding layer 14 with a thickness of 0.5. After successively forming a 1 μm thick GaAs cap layer 15 of 5 p type, an S10 □ film 16 is formed.
, n-type electrode 17, and n-type electrode 18 are formed, SiO with a stripe width of 5 μm and a resonator length of 200 μm is formed by cleavage.
□It is manufactured by using a striped laser and mounting it on the heat sink 19.

The thickness of the active layer as described above is within the range of 0.1 to 0.3μ to ensure sufficient light emission and to emit light with low power consumption.
m, and the thickness of the cladding layer that ensures the optical confinement effect, each having a value within the range of 0.3 to 0.8 μm, so that the optical confinement in the direction perpendicular to the substrate is sufficient and the optical loss is small.

On the other hand, heat generated in the active layer 13 is carried to the heat sink 19 through the cladding layer 12, the substrate 11, and the electrode 18. The thermal resistance of InGaAl F is 10 times higher than that of GaAs substrate.
The thickness of the InGa81P layer determines the heat release efficiency (the thermal resistance of the electrode 18 can be almost ignored). Therefore, compared to conventional semiconductor lasers with a cladding layer of 1 μm or more,
Since the thickness of the cladding layer is reduced to below each level, sufficient heat dissipation is achieved, and when it was actually operated, the oscillation wavelength was 0.
．． A high-performance visible light semiconductor laser capable of continuous oscillation at a low current of 68 μm and a threshold current of 50 mA at room temperature was obtained.

In the above embodiment, In0. <5Ga0. 51-11
81. An active layer consisting of P(0≦X<0.3> and [na, , 5Ga0.s+ provided on each side of the active layer
-yA12 P (X +0.2≦y≦0.51) in the semiconductor laser according to the present invention, which has a composition of x=0. However, as is clear from the graph in Figure 2, even in the composition range of 0 x < 0.3, the refractive index of the active layer is approximately 3.6, while the difference in refractive index between the active layer and the cladding layer is The thickness of the InGaAlP cladding layer on the heat sink side is set to about 0.8~0.2.
It will be clear that it can be 0.3 μm.

As described in detail, according to the present invention, a semiconductor laser made of [nGaAlF lattice-matched to a GaAs substrate continuously oscillates at a low current at room temperature, and therefore can be easily used without the need for a cooling device. I can do it.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a semiconductor laser according to an embodiment of the present invention, and FIG. 2 is an In0. 4sGa0. 51-X to IX
Figure 3 shows the relationship between the refractive index of P and the energy of incident light.
1 is a cross-sectional view of a conventional structure of a semiconductor laser consisting of the following. (Main reference numbers) 1...GaAs substrate, 2...In0.4sGa0. s+-yA]yP cladding layer, 3...In0. 4sGao-s+-xAlx
P active layer, 4' ln0. n5Ga0. s+-yA
12P cladding layer, 5... cap layer, 6.7...
Electrode, 11...n-type GaAs substrate, 12...n-type 1n0. , 5Ga0. 3+AI0.
2Q P cladding layer, 13...In. , <5Ga0
．． s+ P active layer, 14” p ff1ln0.
1sGa0. 31A10.20 P cladding layer, 15
= p-type GaAs key 1'-/p layer, 16 = Si○2 film, 17... n-type electrode, 18... n-type electrode, 19... heat sink

Claims (1)

[Claims] (1) In_0_. _4_9Ga_0_. ＿５＿１＿−
an active layer consisting of _xAl_xP (0≦x<0.3);
In_0_. provided on each side of the active layer. _4_9Ga
＿0＿． _5_1_-_yAl_yP(x+0.2≦y
≦0.51), and is formed to be lattice matched to the GaAs substrate, and the InGa
The thickness of the AlP active layer is 0.1 to 0.3 μm, and the thickness of the InGaAlP cladding layer on the heat sink side is 0.8 μm.
An InGaAlP semiconductor laser characterized in that it has a diameter of ~0.3 μm.